Comparative vascular effects of midazolam and lorazepam administered during cardiopulmonary bypass

We studied the comparative vascular effects of midazolam and lorazepam in 52 patients undergoing elective cardiac surgery procedures. After administration of fentanyl, 100 micrograms/kg intravenously, the patients were randomized to receive either midazolam 0.1 mg/kg (M high), midazolam 0.05 mg/kg (M low), lorazepam 0.1 mg/kg (L high), lorazepam 0.05 mg/kg (L low), or placebo during cardiopulmonary bypass (CPB). Compared to the placebo and L-low groups, the high-dose midazolam group had more effect on systemic vascular resistance (SVR) starting at 5 min after study drug administration (P < 0.02). M high and L high required increased quantities of phenylephrine administered to maintain the mean arterial pressure (MAP) at > 50 mm Hg after rewarming and removal of the aortic cross-clamp (P < 0.03). In the first 12 h of the postoperative period, the M-high group required phenylephrine (PHE) infusion for hypotension associated with decreased SVR more often than placebo (8/10 vs 1/11 patients, P < 0.008, chi 2). In conclusion, midazolam more effectively attenuated the increase in SVR that occurred during CPB than patients receiving either placebo or lorazepam. The hemodynamic effects from a single dose of 0.1 mg/kg midazolam administered at the start of CPB may persist into the postoperative period.